A typical example of the prior art centrifuge of this type is disclosed in Japanese Patent Publication No. 3-34279, a summary of which will be described below.
FIG. 1A shows a rotor chamber 1 and a motor 7 which form a part of the centrifuge. A housing which accommodates these components is not shown. Mounted to the top end of the rotating shaft 7R within the rotor chamber 1 of the centrifuge is a rotor 2 which is rotatively driven by energizing the motor 7. Mounted to the bottom end of the rotor 2 is an adapter 5 having magnets 6 attached thereto on the same circumference at an interval of rotational angle .theta. (FIG. 1B) predetermined depending on the type of rotor.
An annular fixed mount 3 is disposed concentrically around the rotating shaft 7R and has a magnetic sensor 4 mounted in its outer peripheral surface which is in opposed, spaced relation with the inner periphery of the adapter 5. The magnetic sensor 4 is adapted to sense the magnetic flux of the magnets 6 to produce an output signal corresponding to the sensed flux and transmit it to a microcomputer 9 as shown in FIG. 2.
The microcomputer 9 is also provided with an output signal from a rotation sensor or tachometer 8 for sensing the number of revolutions of the motor 7. The microcomputer 9 further determines the operational conditions of the centrifuge such as the number of revolutions per unit time, the time for operation, the time for acceleration, the time for deceleration, the temperature of the rotor, whether the rotor chamber 1 is under vacuum or at an atmospheric pressure, the permissible revolution rate of the rotor itself, etc. to control the operations of an operational condition display 13, the motor 7, a refrigerator 14 and other devices 15 by storing in a RAM 12 or taking out from the RAM the operational data as preset by an operational condition setting device 16, in accordance with a centrifuge controlling program stored in a ROM 11.
Upon the operator depressing a start switch 10, the microcomputer 9 outputs a signal of acceleration to the motor 7 to start rotating it whereupon the magnetic sensor 4 detects the magnetic flux and transmits a corresponding output signal to the microcomputer 9. The microcomputer 9, which has been supplied with signals from the rotation sensor 8 and the magnetic sensor 4, is in turn capable of identifying the type of the associated rotor by calculating the angular spacing .theta. between two magnets on the basis of the pulse period Tr per revolution of the rotor and the interval T.theta. between pulses. If an adapter 5 having a particular mounting angle .theta. peculiar to a particular type of rotor 2 is employed, the microcomputer 9 is able to identify the type of the rotor by determining the angle .theta. formed between the adjacent magnets 6 peculiar to said rotor. Accordingly, the data of the operational conditions for each type of rotor are stored in the RAM 12, and the microcomputer 9 will identify the type of rotor by the value of .theta. and read out the data of the operational conditions for the particular type of rotor to thereby automatically control the operation of the centrifuge.
The conventional centrifuge is equipped with only one magnetic sensor 4 for sensing the magnetic flux of the magnets 6, so that the rotor 2 cannot be identified unless it is rotated. That is, the procedures are in such an order that, when the rotor starts to rotate, the type of the rotor is automatically identified by the centrifuge, the operational conditions are determined on the basis of the operational data (stored in the RAM of the centrifuge) and the operational conditions are indicated on the display 13. The operator cannot know that a wrong rotor is being used before he takes a look at the display. In that case, as the rotor is already rotating, the operator has to turn off the start switch 10 and wait until the rotor 2 stops rotating. The use of a wrong rotor thus results in an undesirable loss in time.
The German Patent Application Publication DE 3815449A1 also discloses a centrifuge capable of automatically identifying the type of rotor. In this apparatus, magnets are arranged on the bottom surface of a rotor along a defined circle at predetermined equal angular intervals and in a polar array defined depending on the type of the rotor, and a single magnetic sensor is disposed at a fixed position opposing and spaced from said circle. The arrangement is such that the type of rotor may be identified in accordance with a bit pattern of "0's" and "1's" detected as the rotor rotates. However, this apparatus is also unable to identify the type of rotor while the rotor is at a standstill, as is the case with the prior Japanese art example as described above.